Arc welding control method

ABSTRACT

In thin sheet welding, when a heat input amount relative to a sheet thickness is too large, a welding defect such as a deviation from aim due to occurrence of a strain or burn through may easily occur. When a welding current is decreased to reduce the heat input amount, there is an issue in which an arc tends to become unstable. In arc welding that repeats short-circuit and arcing, first heat input period (Th) and second heat input period (Tc) having a heat input amount less than that of first heat input period (Th) are periodically repeated. This reduces the heat input amount into a welding object and suppresses burn through and a strain upon welding while making the arc stable.

TECHNICAL FIELD

The present disclosure relates to an arc welding control method ofperforming welding output control of short-circuit arc welding bygenerating an arc between a welding wire that is a consumable electrodeand a base material that is a welding subject.

BACKGROUND ART

Recently, in view of global environmental protection, in an automobileindustry, thinning of a vehicle steel sheet and the like has beenpromoted year by year for weight reduction, in order to improve fueleconomy. Furthermore, improvement of manufacturing tact of a weldingprocess has been promoted for productivity improvement. Therefore, anincrease in welding speed and improvement of welding quality have beendemanded in arc welding of a thin sheet, which is performed using arobot. However, the increase in welding speed and a challenge ofpreventing defects such as burn through and undercut are contrary eachother. Furthermore, when a gap is produced between base materials,suppression of the burn through can improve a yield of a welding object.Therefore, reduction of man hour for modification can be expected. Forthis purpose, demand from the market for achieving those challenges hasbeen growing year by year. In response to those demands, varioustechniques have been conventionally proposed for thin sheet welding andgap welding. For example, in pulse metal active gas (MAG) arc welding, apulse condition such as a pulse current or a base current is switched totwo pulse current groups. This can adjust an arc length (for example,refer to PTL 1). With this configuration, in butt welding or lapwelding, even when a gap is produced, the arc length can be shortened.This can suppress the burn through.

CITATION LIST Patent Literature

PTL 1: Unexamined Japanese Patent Publication No. H04-333368

SUMMARY OF THE INVENTION

However, in recent years in which thinning of a sheet for weightreduction has been promoted, pulse arc welding having a large heat inputamount easily generates penetration beads on a rear side of a weldingsubject in comparison with short-circuit arc welding. This situation ishighly likely to cause the burn through, and further a strain can easilybe produced in the welding subject. The strain thus produced has a moresignificant effect with a longer welding length. A deviation from aim ofa welding wire with respect to the welding subject may occur. Further,when high-speed welding is performed, undercut is easily produced,thereby hindering improvement of productivity. When an entire weldingcurrent is reduced, reduced heat input can be achieved. However, thereis an issue in which an arc becomes unstable.

To solve the above-described issues, an arc welding control methodaccording to the present disclosure is an arc welding control method ofperforming arc welding by periodically repeating a first heat inputperiod having a first heat input amount and a second heat input periodhaving a second heat input amount to a welding subject using a weldingwire that is a consumable electrode, and has the following features.That is, each of the first heat input period and the second heat inputperiod includes a short-circuit period and an arc period. Further, whenrelease of short-circuit is detected during the short-circuit period inthe second heat input period, a welding current after the release of theshort-circuit in the second heat input period is set to be less than acurrent immediately before the release of the short-circuit, and awelding current during the arc period in the second heat input period isset to be less than a welding current during the arc period in the firstheat input period. Alternatively, a total sum of energy indicated by anintegral of the welding current over time during the arc period in thesecond heat input period is set to be less than a total sum of energyindicated by an integral of the welding current over time during the arcperiod in the first heat input period.

Further, an arc welding control method according to the presentdisclosure is an arc welding control method of performing arc welding byperiodically repeating a first heat input period having a first heatinput amount and a second heat input period having a second heat inputamount to a welding subject using a welding wire that is a consumableelectrode, and has the following features. That is, each of the firstheat input period and the second heat input period includes ashort-circuit period and an arc period. Further, when release ofshort-circuit is detected during the short-circuit period in the secondheat input period, a welding current during the arc period in the secondheat input period is set to be less than a current immediately beforethe release of the short-circuit, and is set to be less than a weldingcurrent during the arc period in the first heat input period, so thatthe welding current during the arc period in the second heat inputperiod is relatively decreased from the welding current during the arcperiod in the first heat input period at a predetermined ratio.

In addition to the above, the welding current during the arc period inthe second heat input period is set to be a constant current that isless than the welding current during the arc period in the first heatinput period, and is set to not less than 30 A.

In addition to the above, the first heat input period and the secondheat input period are periodically repeated such that, according to atleast one of a sheet thickness and a gap amount of the welding subject,not less than one time and not more than five times of the first heatinput periods that are successively performed and one time of the secondheat input period are alternately repeated in a periodical manner.

In addition to the above, forward feeding that feeds the welding wiretoward the welding subject and reverse feeding that feeds the weldingwire in a direction opposite to the forward feeding are alternatelyrepeated periodically at a predetermined period and amplitude.

In the present disclosure, by performing short-circuit welding, areduced heat input period that is a second heat input period in which awelding current after release of short-circuit is decreased and a firstheat input period having a larger heat input amount than that of thesecond heat input period are periodically repeated. This can achievereduced heat input while maintaining the stable arc. This can alsoachieve suppression of burn through in thin sheet welding andimprovement of a gap tolerance, thereby being capable of preventingundercut and reducing a strain in high-speed welding. This can improvewelding quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating output waveforms and droplet transferringstates of a tip of a welding wire generated by an arc welding controlmethod according to first and second exemplary embodiments of thepresent disclosure.

FIG. 2 is a diagram illustrating a schematic configuration of an arcwelding device of the present disclosure.

FIG. 3 is a view illustrating output waveforms and droplet transferringstates of a tip of a welding wire generated by an arc welding controlmethod according to a third exemplary embodiment of the presentdisclosure.

FIG. 4 is a view illustrating an output waveform generated by an arcwelding control method according to a fourth exemplary embodiment of thepresent disclosure.

FIG. 5 is a view illustrating an output waveform generated by the arcwelding control method according to the fourth exemplary embodiment ofthe present disclosure.

FIG. 6 is a graph illustrating a relationship between successive repeatcounts Thn of first heat input period Th and gap amount G according tothe fourth exemplary embodiment of the present disclosure.

DESCRIPTION OF EMBODIMENTS

Hereinafter, exemplary embodiments according to the present disclosurewill be described with reference to FIGS. 1 to 6.

First Exemplary Embodiment

First, an arc welding device that performs an arc welding control methodaccording to the present first exemplary embodiment will be describedwith reference to FIG. 2. FIG. 2 is a diagram illustrating a schematicconfiguration of the arc welding device. Arc welding device 20 performswelding by repeating arc period Ta in an arcing state and short-circuitperiod Ts in a short-circuited state between welding wire 22 that is aconsumable electrode and welding object 21 that is a welding subject.

Arc welding device 20 includes main transformer 2, primary rectifier 3,switching unit 4, DCL (reactor) 5, secondary rectifier 6, weldingcurrent detector 7, welding voltage detector 8, short-circuit detector9, short-circuit releasing detector 10, short-circuit/arc detector 11,and wire feeding speed controller 16.

Output controller 12 includes short-circuit controller 13 and arccontroller 14. Wire feeding speed controller 16 includes wire feedingspeed detector 17, operation unit 18, andforward-feeding/reverse-feeding switching timing controller 19. Primaryrectifier 3 rectifies an input voltage input from input power supply 1disposed outside arc welding device 20. Switching unit 4 controls anoutput of primary rectifier 3 to be an output suitable for welding. Maintransformer 2 converts an output of switching unit 4 into an outputsuitable for welding. Secondary rectifier 6 rectifies an output of maintransformer 2. DCL (reactor) 5 smooths an output of secondary rectifier6 to be a current suitable for welding.

Welding current detector 7 detects a welding current. Welding voltagedetector 8 detects a welding voltage. Short-circuit/arc detector 11determines, based on an output of welding voltage detector 8, whether awelding state is a short-circuited state in which welding wire 22 andwelding object 21 are short-circuited to each other or an arcing statein which arc 23 is generated between welding wire 22 and welding object21. Short-circuit releasing detector 10 detects a number of times ofdetermination that the short-circuited state is released to establishthe arcing state.

Output controller 12 outputs a control signal to switching unit 4 tocontrol a welding output. In a case where short-circuit/arc detector 11determines that the short-circuited state is established, short-circuitcontroller 13 controls a short-circuit current that is a welding currentduring a short-circuit period. In a case where short-circuit/arcdetector 11 determines that the arcing state is established, arccontroller 14 controls an arc current that is a welding current duringan arc period. When short-circuit releasing detector 10 detects thenumber of times of short-circuit release set by welding conditionsetting unit 15, arc controller 14 performs control in which a weldingcurrent in a second heat input period is decreased.

Wire feeding speed controller 16 controls wire feeder 25 to control afeeding speed of welding wire 22. Wire feeding speed detector 17 detectsthe wire feeding speed. Operation unit 18 operates a predetermined timeand an integrated amount of a feeding amount of welding wire 22 based ona signal from wire feeding speed detector 17.Forward-feeding/reverse-feeding switching timing controller 19 outputs acontrol signal that delays switching timing from forward feeding toreverse feeding and a control signal that delays switching timing fromthe reverse feeding to the forward feeding, of feed of welding wire 22,based on a signal from operation unit 18.

Welding condition setting unit 15 and wire feeder 25 are connected toarc welding device 20. Welding condition setting unit 15 is used to seta welding condition to arc welding device 20. Wire feeder 25 performscontrol of feed of welding wire 22 based on a signal from wire feedingspeed controller 16.

A welding output of arc welding device 20 is supplied to welding wire 22via welding tip 24. The welding output of arc welding device 20 thengenerates arc 23 between welding wire 22 and welding object 21 toperform welding.

Next, an operation of arc welding device 20 thus configured will bedescribed with reference to FIG. 1.

FIG. 1 is a view illustrating output waveforms generated by an arcwelding control method of a consumable electrode type according to thepresent exemplary embodiment. FIG. 1 illustrates output waveforms forperforming arc welding that periodically repeats first heat input periodTh having a first heat input amount and second heat input period Tchaving a second heat input amount, to welding object 21 using weldingwire 22 that is a consumable electrode.

Each of first heat input period Th and second heat input period Tcincludes short-circuit period Ts and arc period Ta. FIG. 1 illustratestemporal changes of welding current Aw and welding voltage Vw, andschematic views Ww of droplet transferring states of welding wire 22, inarc welding that alternately repeats short-circuit period Ts and arcperiod Ta, in each of first heat input period Th and second heat inputperiod Tc.

In the arc welding control method according to the present exemplaryembodiment, first heat input period Th and second heat input period Tcare alternately repeated. Each of first heat input period Th and secondheat input period Tc includes short-circuit period Ts and arc period Ta.

During short-circuit period Ts in first heat input period Th, weldingcurrent Aw is increased from a predetermined current value at firstcurrent increase rate Aws1, and reaches current value Awp at a bentpoint described below. Welding current Aw is then increased at currentincrease rate Aws2 that is smaller than current increase rate Aws1.During this short-circuit period Ts, the feeding speed of welding wire22 is set to be negative, and the welding wire is reversely fed. Duringthis short-circuit period Ts, welding wire 22 and welding object 21 areshort-circuited and therefore welding voltage Vw becomes a value closeto 0 (V).

At switching timing from short-circuit period Ts to arc period Ta infirst heat input period Th, welding current Aw is temporarily decreased,thereby increasing welding voltage Vw due to the release of theshort-circuit. Feeding speed Wf of welding wire 22 is switched from anegative value to a positive value. This switches the feed of thewelding wire from the reverse feeding to the forward feeding.

During arc period Ta in first heat input period Th, welding current Awis increased to peak current value Awa1, and is kept constant for apredetermined time.

At end timing of arc period Ta in first heat input period Th and atstart timing of short-circuit period Ta in second heat input period Tc,welding current Aw is decreased to a predetermined value and weldingwire 22 and welding object 21 are short-circuited. Therefore, weldingvoltage Vw becomes a value close to 0 (V) and feeding speed Wf ofwelding wire 22 is switched from a positive value to a negative value.This switches the feed of the welding wire from the forward feeding tothe reverse feeding.

During short-circuit period Ts in second heat input period Tc, weldingcurrent Aw is increased from the predetermined value at a predeterminedcurrent increase rate. Welding current Aw is then increased at currentincrease rate Aws2. During this short-circuit period Ts, feeding speedWf of welding wire 22 is set to be negative, and the welding wire isreversely fed.

During arc period Ta in second heat input period Tc, welding wire 22 isshort-circuited. Welding current Aw at this time is set to current valueAwa1 a. During this arc period Ta, feeding speed Wf of welding wire 22is set to be positive, and the welding wire is forwardly fed.

In FIG. 1, each of parts (a) to (h) shows droplet transferring state Wwin which welding metal is transferred from a tip of welding wire 22 thatis a consumable electrode toward welding object 21, and indicates astate of welding wire 22 from first heat input period Th to second heatinput period Tc. Time lapses from part (a) to part (h) in this order.Part (a) indicates the state of welding wire 22 during short-circuitperiod Ts in first heat input period Th. Part (b) indicates the state ofwelding wire 22 at switching timing from short-circuit period Ts to arcperiod Ta in first heat input period Th. Parts (c) and (d) indicate thestates of welding wire 22 during arc period Ta in first heat inputperiod Th. Part (c) indicates the state of welding wire 22 immediatelyafter the value of welding current Aw reaches Awa1. Further, part (d)indicates the state of welding wire 22 immediately before the value ofwelding current Aw is decreased from Awa1. Part (e) indicates the stateof welding wire 22 during short-circuit period Ts in second heat inputperiod Tc. Part (f) indicates the state of welding wire 22 at switchingtiming from short-circuit period Ts to arc period Ta in second heatinput period Tc. Parts (g) and (h) indicate the states of welding wire22 during arc period Ta in second heat input period Tc.

Note that, with respect to transition from arc period Ta in first heatinput period Th to short-circuit period Ts in second heat input periodTc, welding current Aw during arc period Ta in first heat input periodTh is decreased immediately before the transition to short-circuitperiod Ts, thereby suppressing occurrence of a spatter due to theshort-circuit. When an effect of occurrence of a spatter due to theshort-circuit is negligible, the current immediately before thetransition to short-circuit period Ts is not necessarily furtherdecreased immediately before the transition.

First, in droplet transferring state Ww in part (a) of FIG. 1, afterwelding wire 22 and welding object 21 are short-circuited, droplet 26 ofwelding wire 22 is transferred into a welding pool (not illustrated) onwelding object 21. At this time, welding wire 22 is fed with the reversefeeding in a direction opposite to the forward feeding that is performedtoward welding object 21, thereby mechanically prompting the release ofthe short-circuit. Further, to release this short-circuit, weldingcurrent Aw in part (a) is controlled so as to be increased with thelapse of time.

As illustrated in FIG. 1, for example, this welding current Aw isincreased in such a manner that welding current Aw during short-circuitperiod Ts is first increased at first current increase rate Aws1, and isthen increased at second current increase rate Aws2 whose inclination ismore moderate than that of first current increase rate Aws1. Currentvalue Awp when first current increase rate Aws1 is switched to secondcurrent increase inclination Aws2 is referred to as the bent point. Avalue of this bent point is set to a value obtained in advance fromexperiments.

Next, welding voltage Vw in part (b) is increased due to the release ofthe short-circuit between welding wire 22 and welding object 21, wherebythe release of the short-circuit is determined. In droplet transferringstate Ww in part (b) at this time, a constriction phenomenon is causednear the tip of welding wire 22 by the pinch effect, therebytransferring droplet 26. The short-circuit is thus released. Weldingcurrent Aw during a period from part (c) to part (d) is controlled so asto be increased to predetermined peak current value Awa1 during arcperiod Ta. With respect to the feed of welding wire 22 at this time, theforward feeding that feeds welding wire 22 toward welding object 21 isperformed. With this configuration, in droplet transferring states Wwduring the period from part (c) to part (d), a welding speed of the tipof welding wire 22 is increased, and droplet 26 that is melted metal tobe transferred to welding object 21 is formed and grown at the tip ofwelding wire 22. Droplet 26 thus grown is short-circuited again, whichallows droplet 26 to be transferred to welding object 21. Typically, thewelding is performed by repeating only first heat input period Thincluding short-circuit period Ts and arc period Ta through the droplettransferring states illustrated in parts (a), (b), (c), (d).

However, according to the present exemplary embodiment, in FIG. 1, thewelding is performed by periodically repeating first heat input periodTh through the states illustrated in parts (a), (b), (c), and (d) andsecond heat input period Tc through the states illustrated in parts (e),(0, (g), and (h). Second heat input period Tc has a heat input amountless than that of first heat input period Th. This configuration reducesa heat input amount to welding object 21. For example, as illustrated inFIG. 1, in first heat input period Th, after droplet 26 at the tip ofwelding wire 22 is grown through the states illustrated in parts (a),(b), (c), and (d), when occurrence of next short-circuit between weldingwire 22 and welding object 21 is detected from welding voltage Vw inFIG. 1, droplet 26 of welding wire 22 is transferred to the welding poolin droplet transferring state Ww in part (e), similar to droplettransferring state Ww in part (a). Further, to release theshort-circuit, welding current Aw in part (e) is controlled so as to beincreased with the lapse of time, similar to the increase manner ofwelding current Aw in part (a).

Furthermore, in droplet transferring state Ww in part (0 when therelease of the short-circuit is determined from welding voltage Vw insecond heat input period Tc, a constriction phenomenon is caused nearthe tip of welding wire 22 by the pinch effect, thereby transferringdroplet 26 to the welding pool, similar to droplet transferring state Wwin part (b). The short-circuit is thus released. When the release of theshort-circuit is detected in second heat input period Tc, weldingcurrent Aw during arc period Ta in second heat input period Tc, which isindicated in parts (g) and (h), is set to be less than current Asoimmediately before the release of the short-circuit to control weldingcurrent Aw during arc period Ta in second heat input period Tc to be acurrent less than welding current Aw during arc period Ta in first heatinput period Th. Alternatively, the total sum of energy indicated by anintegral of welding current Aw over time during arc period Ta in secondheat input period Tc is controlled to be less than the total sum ofenergy indicated by an integral of welding current Aw over time duringarc period Ta in first heat input period Th. This can reduce the heatinput amount in second heat input period Tc.

Note that, when welding current Aw during arc period Ta in second heatinput period Tc is controlled to be the current less than weldingcurrent Aw during arc period Ta in first heat input period Th, weldingcurrent Aw during arc period Ta in second heat input period Tc ispreferably controlled to be less than peak current Awa1 during arcperiod Ta in first heat input period Th. This can further reduce theheat input amount in second heat input period Tc.

Further, welding current Aw during arc period Ta in second heat inputperiod Tc, which is decreased from welding current Aw during arc periodTa in first heat input period Th, preferably has a value not less than30 A. When welding current Aw during arc period Ta in second heat inputperiod Tc is less than 30 A and continues for a long time, for example,not less than 20 msec, the arc may not be maintained, thereby causingarc interruption. Alternatively, there may be a case in which a size ofdroplet 26 at the tip of welding wire 22 is not grown, thereby hinderingthe release of the short-circuit, to prolong next short-circuit periodTs and cause disorder of the short-circuit period. Therefore, it ispreferable that welding current Aw during arc period Ta in second heatinput period Tc is set to not less than 30 A.

Note that, as in the present disclosure, the welding is performed atfeeding speed Wf that periodically feeds welding wire 22, by switchingfeed at the predetermined period and amplitude to the forward feedingthat feeds welding wire 22 toward welding object 21 and the reversefeeding that feeds welding wire 22 in a direction opposite to theforward feeding. Therefore, occurrence and release of the short-circuitcan be promoted mechanically. First heat input period Th and second heatinput period Tc having a heat input amount less than that of first heatinput period Th are periodically repeated. This can achieve reduced heatinput while maintaining the stable arc. This can also achieve thesuppression of burn through in thin sheet welding and the improvement ofa gap tolerance described later.

Accordingly, even when the heat input amount varies between first heatinput period Th and second heat input period Tc, disorder of theshort-circuit periods can be prevented.

Second Exemplary Embodiment

The present second exemplary embodiment relates to decrease of weldingcurrent Aw after the release of the short-circuit in second heat inputperiod Tc.

Note that, in the present second exemplary embodiment, componentsidentical to components of the first exemplary embodiment are denoted bythe same reference numerals or symbols, and detailed descriptionsthereof are omitted. A main point different from the first exemplaryembodiment is that, as illustrated in FIG. 1, welding current Aw duringarc period Ta in second heat input period Tc to be set to be less thanwelding current Aw during arc period in first heat input period iscontrolled to be predetermined constant current Awa1 a. Note that,constant current Awa1 a is a current that is less than peak current Awa1of welding current Aw during arc period Ta in first heat input periodTh. The control is performed with the constant current until nextshort-circuit occurs, whereby adjustment or management for decreasingthe current is easily conducted.

Third Exemplary Embodiment

The present third exemplary embodiment relates to decrease of thewelding current during arc period Ta in second heat input period Tc.

Note that, in the present third exemplary embodiment, componentsidentical to components of the first and second exemplary embodimentsare denoted by the same reference numerals or symbols, and detaileddescriptions thereof are omitted. A main point different from the firstand second exemplary embodiments is that, as in welding current Awillustrated in FIG. 3, welding current Aw during arc period Ta in secondheat input period Tc is relatively decreased in comparison with thecurrent waveform of welding current Aw during arc period Ta in firstheat input period Th. In comparison with the current waveform of weldingcurrent Aw during arc period Ta in first heat input period Th, weldingcurrent Aw during arc period Ta in second heat input period Tc is madeto have a current waveform that is relatively decreased from weldingcurrent Aw during arc period Ta in second heat input period Tc in asubstantially similar shape. Specifically, welding current Aw during arcperiod Ta in second heat input period Tc is relatively decreased fromcurrent Aw during arc period Ta in first heat input period Th at apredetermined ratio.

With this configuration, welding current Aw during arc period Ta insecond heat input period Tc is the decreased welding current, but haspeak current Awa1 b. Similar to the droplet transferring state in firstheat input period Th that controls the peak current of welding currentAw during arc period Ta to be peak current Awa1, stability of the arc atswitching timing from first heat input period Th to second heat inputperiod Tc can be improved, whereby the reduced heat input can beachieved.

The predetermined ratio, at which welding current Aw in second heatinput period Tc is relatively decreased from welding current Aw in firstheat input period Th, is not less than 10% and not more than 50% ofwelding current Aw during arc period Ta in first heat input period Th.When a degree of decrease from welding current Aw during arc period Tain first heat input period Th is further increased and the relativeratio is decreased so as to be less than 10%, arc interruption is highlylikely to occur in part (h) of FIG. 3 after peak current Awa1 b duringarc period Ta in second heat input period is output in part (g). Incontrast, when the degree of decrease from welding current Aw during arcperiod Ta in first heat input period Th is further decreased and therelative ratio is increased so as to be more than 50%, an effect ofreduced heat input is decreased.

Fourth Exemplary Embodiment

A fourth exemplary embodiment relates to a method of periodicallyrepeating first heat input period Th and second heat input period Tc.

Note that, in the present fourth exemplary embodiment, componentsidentical to components of the first to third exemplary embodiments aredenoted by the same reference numerals or symbols, and detaileddescriptions thereof are omitted. A main point different from the firstto third exemplary embodiments is that, in contrast to the first,second, third exemplary embodiments that repeat one time of first heatinput period Th and one time of second heat input period Tc, the presentexemplary embodiment repeats a plurality of times of first heat inputperiod Th (Th1 to Th5) and one time of second heat input period Tc,according to a sheet thickness of welding object 21 such as a thinsheet.

Welding current Aw in FIG. 4 periodically repeats the plurality of timesof first heat input period Th (Th1 to Th5) and one time of second heatinput period Tc. When it is assumed that successive repeat counts offirst heat input period Th is Thn and successive repeat counts of secondheat input period Tc is Tcn, in a case where Thn is set to five and Tcnis set to one, five times of first heat input period Th and one time ofsecond heat input period Tc are alternately repeated. In FIG. 5, thesuccessive repeat counts of first heat input period Th satisfies Thn=1,and the successive repeat counts of second heat input period Tcsatisfies Tcn=1. One time of first heat input period Th and one time ofsecond heat input period Tc are repeated. An effect for reducing a heatinput amount into welding object 21 becomes higher, with reducedsuccessive repeat counts Thn of the first heat input period. In otherwords, with welding object 21 having a reduced sheet thickness (forexample, 3.2 mm or less), successive repeat counts Thn of first heatinput period Th is preferably small. Therefore, the heat input amountinto welding object 21 can be further reduced.

However, when successive repeat counts Thn in first heat input period Thexceeds five, the heat input amount is relatively increased. Therefore,the effect for reducing the heat input amount is decreased. Furthermore,when successive repeat counts Tcn of second heat input period Tc exceedsone, successive second heat input periods Tc is likely to cause unevenshort-circuit periods Ts in subsequent first heat input period Th,thereby making the arc unstable. Accordingly, the plurality of times offirst heat input period Th of not less than one time and not more thanfive times and one time of second heat input period Tc that arealternately repeated can reduce the heat input amount while maintainingthe stable arc. This leads to suppression of burn through andimprovement of a gap tolerance.

For example, FIG. 6 illustrates a relationship between successive repeatcounts Thn of first heat input period Th and gap amount G, when weldingcurrent Aw during arc period Ta in second heat input period Tc iscontrolled to be constant current Awa1 a as illustrated in FIGS. 4 and5. Note that, in FIG. 6, successive repeat counts Tcn of second heatinput period Tc is set to 1, and a material of welding wire 22 and amaterial of welding object 21 are set to mild steel. For example, forlap welding, a ratio of a gap that is a clearance between sheets to beoverlapped with each other to an average sheet thickness of sheets to beirradiated with the arc, of welding object 21, is defined as gap amountG [%], and a case of the gap being identical to the sheet thickness isexpressed by gap amount G=100%. Successive repeat counts Thn of firstheat input period Th is set to decrease with increased gap amount G.This can improve the gap tolerance. When gap amount G is 100%,successive repeat counts Thn of first heat input period Th is two, andwhen gap amount G is 20%, successive repeat counts Thn of first heatinput period Th is five.

As described above, in the short-circuit welding that repeats theshort-circuit and the arcing, according to the sheet thickness and/orgap amount G of welding object 21, the welding is performed byperiodically repeating one time or more of first heat input periods Ththat are successively repeated and one time of second heat input periodTc having a heat input amount less than that of first heat input periodTh. This can achieve reduced heat input while maintaining the stablearc. This can also achieve the suppression of burn through in the thinsheet welding and the improvement of the gap tolerance, thereby leadingto improvement of welding quality and productivity.

As described above, according to the invention of the presentdisclosure, in the short-circuit welding that repeats the short-circuitand the arcing, by periodically repeating first heat input period Th andsecond heat input period Tc having the heat input amount less than thatof first heat input period Th, it is possible to achieve reduced heatinput while maintaining the stable arc. This can also achievesuppression of burn through in the thin sheet welding and improvement ofthe gap tolerance.

As described above, the ratio between first heat input periods Th andone time of second heat input period Tc having the heat input amountless than that of first heat input period Th is set. Therefore,switching of the heat input amount for the reduced heat input can be setfinely. Moreover, the reduced heat input can be achieved, andfluctuation of bead width can be suppressed, thereby being capable ofacquiring excellent bead external appearance. In the short-circuit arcwelding of the present disclosure, the heat input amount is lower thanthat of the pulse arc welding, and therefore shortening of an arc lengthand reduction of the heat input amount can be achieved.

With those configurations, the welding current during the arc period isperiodically decreased to improve safety of the arcing. The heat inputamount is suppressed and the arc length is shortened to prevent undercutduring high-speed welding. By suppressing the heat input amount, it ispossible to reduce a strain and prevent burn through, during, inparticular, welding of the thin sheet with a gap present between weldingobjects. This can improve welding quality and productivity.

INDUSTRIAL APPLICABILITY

According to the invention of the present disclosure, in short-circuitwelding in which short-circuit and arcing are repeated, by periodicallyrepeating first heat input period Th and second heat input period Tchaving a heat input amount less than that of first heat input period Th,it is possible to achieve reduced heat input while maintaining thestable arc. This can also achieve suppression of burn through in thinsheet welding and improvement of a gap tolerance, thereby leading toimprovement of welding quality and productivity. These arc weldingcontrol methods are industrially useful as an arc welding control methodof performing short-circuit arc welding while feeding a welding wirethat is a consumable electrode.

REFERENCE MARKS IN THE DRAWINGS

-   -   1 input power supply    -   2 main transformer    -   3 primary rectifier    -   4 switching unit    -   5 DCL (reactor)    -   6 secondary rectifier    -   7 welding current detector    -   8 welding voltage detector    -   9 short-circuit detector    -   10 short-circuit releasing detector    -   11 short-circuit/arc detector    -   12 output controller    -   13 short-circuit controller    -   14 arc controller    -   15 welding condition setting unit    -   16 wire feeding speed controller    -   17 wire feeding speed detector    -   18 operation unit    -   19 forward-feeding/reverse-feeding switching timing controller    -   20 arc welding device    -   21 welding object    -   22 welding wire    -   23 arc    -   24 welding tip    -   25 wire feeder    -   26 droplet

1. An arc welding control method of performing arc welding byperiodically repeating a first heat input period having a first heatinput amount and a second heat input period having a second heat inputamount to a welding subject using a welding wire that is a consumableelectrode, wherein each of the first heat input period and the secondheat input period includes a short-circuit period and an arc period, andwhen release of short-circuit is detected during the short-circuitperiod in the second heat input period, a welding current during the arcperiod in the second heat input period is set to be less than a currentimmediately before the release of the short-circuit, and the weldingcurrent during the arc period in the second heat input period is set tobe less than a welding current during the arc period in the first heatinput period, or a total sum of energy indicated by an integral of thewelding current over time during the arc period in the second heat inputperiod is set to be less than a total sum of energy indicated by anintegral of the welding current over time during the arc period in thefirst heat input period.
 2. An arc welding control method of performingarc welding by periodically repeating a first heat input period having afirst heat input amount and a second heat input period having a secondheat input amount to a welding subject using a welding wire that is aconsumable electrode, wherein each of the first heat input period andthe second heat input period includes a short-circuit period and an arcperiod, and when release of short-circuit is detected during theshort-circuit period in the second heat input period, a welding currentduring the arc period in the second heat input period is set to be lessthan a current immediately before the release of the short-circuit, andis set to be less than a welding current during the arc period in thefirst heat input period, so that the welding current during the arcperiod in the second heat input period is relatively decreased from thewelding current during the arc period in the first heat input period ata predetermined ratio.
 3. The arc welding control method according toclaim 1, wherein the welding current during the arc period in the secondheat input period is set to be a constant current that is less than thewelding current during the arc period in the first heat input period,and is set to not less than 30 A.
 4. The arc welding control methodaccording to claim 1, wherein the first heat input period and the secondheat input period are periodically repeated such that, according to atleast one of a sheet thickness and a gap amount of the welding subject,not less than one time and not more than five times of the first heatinput periods that are successively performed and one time of the secondheat input period are alternately repeated periodically.
 5. The arcwelding control method according to claim 1, wherein forward feedingthat feeds the welding wire toward the welding subject and reversefeeding that feeds the welding wire in a direction opposite to theforward feeding are alternately repeated periodically at a predeterminedperiod and amplitude.
 6. The arc welding control method according toclaim 2, wherein the welding current during the arc period in the secondheat input period is set to be a constant current that is less than thewelding current during the arc period in the first heat input period,and is set to not less than 30 A.
 7. The arc welding control methodaccording to claim 2, wherein the first heat input period and the secondheat input period are periodically repeated such that, according to atleast one of a sheet thickness and a gap amount of the welding subject,not less than one time and not more than five times of the first heatinput periods that are successively performed and one time of the secondheat input period are alternately repeated periodically.
 8. The arcwelding control method according to claim 2, wherein forward feedingthat feeds the welding wire toward the welding subject and reversefeeding that feeds the welding wire in a direction opposite to theforward feeding are alternately repeated periodically at a predeterminedperiod and amplitude.